Abstract
We studied the xylem hydraulic traits and anatomy of four diverse Mediterranean
conifers to determine how these species protect themselves against catastrophic xylem
failure. Cedrus atlantica, Cupressus sempervirens, Pinus nigra and P.
halepensis
seedlings were grown for two years in pots in a greenhouse under well-watered
conditions. Measurements were conducted in April and September. The vulnerability to
cavitation was lower in April in the two pines and cedar whereas the conductivity was lower
in the two pines and cypress. There were also large species differences in vulnerability to
cavitation in September: loss of 50% conductivity occurred at -2.8 MPa in P. nigra,
-3.8 MPa in C. atlantica, -4.8 MPa in C. sempervirens and -4.9 MPa in P.
halepensis
. Leaf specific hydraulic conductivity was much higher in Cupressus sempervirens
and P. nigra than in Cedrus atlantica and P. halepensis. No trade-off
between xylem safety (low vulnerability) and efficiency (high hydraulic conductivity) was
found among the four species. Specific conductivity was directly related to "hydraulic mean"
tracheid lumen diameter, while xylem vulnerability appeared to be independent of tracheid
size.